The following related patent applications, assigned to the same assignee hereof and filed on even date herewith in the names of the same inventors as the present application, disclose related subject matter, with the subject of each being incorporated by reference herein in its entirety:
Memory Module with Hierarchical Functionality, Ser. No. 09/775,477; High Precision Delay Measurement Circuit, Ser. No. 09/776,262; Single-Ended Sense Amplifier with Sample-and-Hold Reference, Ser. No. 09/776,220; Limited Switch Driver Circuit, Ser. No. 09/775,478; Fast Decoder with Asynchronous Reset with Row Redundancy; Ser. No. 09/775,476; Diffusion Replica Delay Circuit, Ser. No. 09/776,029; Sense Amplifier with Offset Cancellation and Charge-Share Limited Swing Drivers, Ser. No. 09/775,475; Memory Architecture with Single-Port Cell and Dual-Port (Read and Write) Functionality, Ser. No. 09/775,701; Memory Redundancy Implementation, Ser. No. 09/776,263; and; A Circuit Technique for High Speed Low Power Data Transfer Bus, Ser. No. 09/776,028.
1. Field of the Invention
The present invention relates to memory devices, in particular, semiconductor memory devices, and most particularly, scalable, power-efficient semiconductor memory devices.
2. Background of the Art
Memory structures have become integral parts of modern VLSI systems, including digital signal processing systems. Although it typically is desirable to incorporate as many memory cells as possible into a given area, memory cell density is usually constrained by other design factors such as layout efficiency, performance, power requirements, and noise sensitivity.
In view of the trends toward compact, high-performance, high-bandwidth integrated computer networks, portable computing, and mobile communications, the aforementioned constraints can impose severe limitations upon memory structure designs, which traditional memory system and subcomponent implementations may fail to obviate.
One type of basic storage element is the static random access memory (SRAM), which can retain its memory state without the need for refreshing as long as power is applied to the cell. In an SRAM device, the memory state II usually stored as a voltage differential within a bistable functional element, such as an inverter loop. A SRAM cell is more complex than a counterpart dynamic RAM (DRAM) cell, requiring a greater number of constituent elements, preferably transistors. Accordingly, SRAM devices commonly consume more power and dissipate more heat than a DRAM of comparable memory density; thus efficient, lower-power SRAM device designs are particularly suitable for VLSI systems having need for high-density SRAM components, providing those memory components observe the often strict overall design constraints of the particular VLSI system. Furthermore, the SRAM subsystems of many VLSI systems frequently are integrated relative to particular design implementations, with specific adaptions of the SRAM subsystem limiting, or even precluding, the scalability of the SRAM subsystem design. As a result SRAM memory subsystem designs, even those considered to be xe2x80x9cscalablexe2x80x9d, often fail to meet design limitations once these memory subsystem designs are scaled-up for use in a VLSI system with need for a greater memory cell population and/or density.
There is a need for an efficient, scalable, high-performance, low-power memory structure that allows a system designer to create a SRAM memory subsystem that satisfies strict constraints for device area, power, performance, noise sensitivity, and the like. In addition, a memory redundancy implementation also is needed.
A first embodiment of the invention is useful in a memory module having a designated group of memory cells assigned to represent a logical portion of the memory structure. In such an environment, a memory redundancy circuit is provided comprising a redundant group of memory cells, and a redundancy controller coupled with the designated group and the redundant group. The redundancy controller assigns the redundant group to the logical portion of the memory structure, and is responsive to a preselected memory group condition.
A second embodiment of the invention includes a memory circuit comprising pairs of designated memory cells, pairs of redundant memory cells, and a controller that redirects a signal path from the designated memory cells to the redundant memory cells based on a failure of the designated memory cells.
A third embodiment of the invention includes a memory circuit comprising designated memory cells, redundant memory cells, and a controller that redirects a signal path from the desingated memory cells to the redundant memory cells based on a failure of the designated memory cells. The controller comprises a plurality of selectable switches having a logarithmic relationship to the number of designated memory cells.